1. Field of the Invention
This invention relates to a method for a determination of an ion concentration, specific gravity, or osmotic pressure of a solution and to an apparatus for use in the determination.
2. Description of the Prior Art
The determination of the specific gravity of a solution is widely practiced in the field of food industry, fermentation industry, or clinical test. In the field of clinical test, for example, the diagnosis of a renal disease by the determination of the specific gravity of a given patient's urine is in vogue. The specific gravity of urine represents the amount of a solute present in the urine and constitutes itself a useful barometer of the renal function. It is known that the magnitude of this specific gravity shows a satisfactory correlation with the ion concentration and osmotic pressure of urine. Generally, the specific gravity of urine from a healthy man falls in the range of 1.016 to 1.022. A specific gravity smaller than the lower limit of this range is a good reason for suspecting diabetes insipidus, acute renal failure, myelitis, etc. Conversely, a specific gravity larger than the upper limit of the range offers a convincing reason for suspecting nephrotic syndrome, various forms of abnormal loss of water, etc. Heretofore, it has been customary to determine the specific gravity of urine by the use of a pycnometer or a hydrometer or by the use of a urine refractometer or an osmometer which has a correlative bearing upon urine specific gravity.
The method which attains the determination with a pycrometer or a hydrometer, for example, however has been variously problematic as in respect that it necessitates an expensive measuring instrument, that it inevitably requires the measuring instrument to be sparingly susceptable to breakage, and that it suffers the measuring instrument to involve a complicated procedure. In the measures heretofore proposed for the solution of this problem, (A) a composition for the determination of specific gravity or osmolality of a given sample liquid, which composition comprises a substance capable of producing a discernible response as the function of the specific gravity or osmolality of the liquid and at least an effective number of microcapsules having the aforementioned substance hermetically contained therein and possessing a wall of a polymeric membrane translucent and susceptible of fracture under the pressure due to permeation and, therefore, operates by causing the contained substance to be released through the wall of membrane on the occurrence of a prescribed osmotic pressure gradient through the interior and exterior of the microcapsules and allowing the released substance to produce the discernible response and a measuring instrument formed by the use of the composition [JP-B-60-46,374(1985)], (B) a composition for the determination of the ionic strength of a liquid sample, which composition comprises a weakly acidic or weakly basic polyvalent macromolecular electrolyte and a pH supporting substance capable of inducing a discernible response during the course of ion exchange between the electrolyte and the liquid sample [JP-B-62-12,858(1987)], and (C) a device for testing a sample aqueous solution for specific gravity, which comprises a wettable substance exhibiting a capacity for absorption corresponding to the ion strength of the aqueous solution, a test layer containing an absorption indicating substance exhibiting solubility corresponding to the magnitude of variation in the capacity for absorption and consequently producing a change in transparency, and a supporting member serving as an optical background for the test layer [JP-A-62-95,462(1987)] have been renowed.
The methods using the compositions of (A), (B), and (C), however, invariably entail the disadvantage that the determination turns out to be expensive, complicated operationally, and deficient in accuracy.
As object of this invention, therefore, is to provide a novel method for the determination of the ion concentration, specific gravity, or osmotic pressure of a solution and an apparatus to be used in the determination.